(1) Field of the Invention
The present invention relates to the use of thermal barrier coatings containing high concentrations of sodium containing compounds in the form of a dopant, second phase, or, as discrete layer(s) in the coating.
(2) Prior Art
Turbine engine airfoils used in desert environments may degrade due to sand related distress of thermal barrier coatings. The mechanism for such distress is the penetration of fluid sand deposits into 7YSZ ceramic thermal barrier coatings that leads to spallation and then accelerated oxidation of exposed metal. It has been observed that gadolinia stabilized zirconia coatings react with fluid sand deposits and a reaction product forms that inhibits fluid sand penetration into the coating. The reaction product has been identified as being a silicate oxyapatite/garnet containing primarily gadolinia, calcia, zirconia, and silica.
One way of improving airfoil efficiency is to reduce surface roughness. Sealant layers have been used to address this issue.
There remains a need however for a coating system which effectively deals with sand related distress.